There is known a plating device in which a substrate of a semiconductor wafer or the like is held in a substrate holder and the substrate is immersed into a plating solution in a plating tank. As shown in FIG. 18, the substrate holder includes a plurality of internal contacts 100 that come into contact with the circumferential edge of a substrate W, and a plurality of external contacts 101 respectively connected to the internal contacts 100. Wires 104 connecting between the plurality of internal contacts 100 and the plurality of external contacts 101 are disposed inside the substrate holder. The external contact 101 is brought into contact with a power feed terminal 103 connected to a power source 105 when the substrate holder is disposed in a predetermined position in the plating tank. A current flows to the substrate W through the external contact 101 and the internal contact 100, and a metal film is formed on the surface of the substrate W in the presence of the plating solution.
When electric resistance between a certain internal contact 100 and the substrate W (hereinafter simply referred to as electric resistance of the internal contact 100) is extremely high or extremely low, currents flowing in the plurality of internal contacts 100 become non-uniform, which may cause a problem with the uniformity of the film thickness within the substrate surface. There have thus been techniques in which a value of resistance against a current, flowing from the internal contact of the substrate holder to the substrate being a plating object, is measured in a state where the substrate is held in the substrate holder, to test the substrate and the substrate holder (for example, Japanese Patent Laid-Open No. 2015-200017 and Japanese Patent Laid-Open No. 2005-146399).